package/dmraid: fix compilation under musl

Fixes:
http://autobuild.buildroot.net/results/feb/feb731da1d865b82781366798ffa8aaf40cf2ec4/
http://autobuild.buildroot.net/results/fcf/fcf1ea738da90016900c04313cdcb3a02658e953/
http://autobuild.buildroot.net/results/385/385e07e9097d877cd1babdd4133fbe14a8f217d9/



.. and others.

Note, upstream package appears dormant.

Signed-off-by: Brendan Heading <brendanheading@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>